Cancer, a leading cause of death worldwide, comprises a group of diseases, which are caused by genetic disorders resulting from genomic instability. It has been postulated that all cancer cells harbour defects in several regulatory pathways, which govern normal cell proliferation and homeostasis. Theses defects result in acquirement of various cancer cell specific hallmark capabilities (Hanahan and Weinberg, 2000, Cell 100, 57-70). One of these hallmarks of cancer is evasion of apoptosis or programmed cell death, an evolutionary conserved program of cellular suicide (Hengartner, 2000, Nature 407, 770-776.). Apoptosis is essential in fetal development by removal of cells not needed any longer, and maintenance of homeostasis of adult tissues by balancing cell production and cell elimination. Additionally, cells exhibiting aberrant features like mutations or genomic damages induced by infectious agents or drugs are removed in this way. In malignant cells this cellular surveillance is missing due to inhibition of apoptosis, which results in extended cell viability increasing the risk of cellular transformation, accelerated disease progression and resistance to therapy (Evan and Vousden, 2001, Nature 411, 342-348. Therefore, manipulation of apoptosis has emerged as a new therapeutic strategy for treatment of cancer (Nicholson D W, 2000, Nature 407, 810-816).
Two signaling pathways leading to induction of apoptosis are known, the intrinsic or mitochondrial pathway, induced by environmental stress and chemotherapeutics, and the extrinsic or death receptor pathway, induced by effector cells of the immune system (Ashkenazi and Dixit, 1998 Science 281, 1305-1308; Green and Reed, 1998, Science 281, 1309-1312). Both pathways culminate with the activation of caspases, a family of intracellular cystein proteases, which within minutes dismantle the cell's structures leading to rapid cell death (Cohen, 1997, Biochem J 326, 1-16). Both, apoptosis promoting as well as inhibiting proteins are known. The Bcl-2 protein family comprises both, pro- and anti-apoptotic proteins. Among the inhibitors of apoptosis, the evolutionary highly conserved inhibitor of apoptosis protein (IAP) family comprises eight proteins in humans. One of them, survivin, has only recently been identified (Ambrosini et al., 1997, Nat. Med. 3, 917-921). Survivin inhibits apoptosis downstream of Bcl-2 by directly or indirectly inhibiting the effector caspase −3 and −7 intracellular proteases responsible or apoptosis (Shin et al., 2001, Biochemistry 40, 1117-1123) Recent evidence suggests that survivin directly controls the activation of the upstream acting caspase 9. A survivin Thr34-Ala dominant negative mutant fails to induce apoptosis in mouse embryonic fibroblasts deficient in apoptosome components Apaf-1 or caspase 9 (Blanc-Brude et al., 2003, Clin. Cancer Res. 9, 2683-2692) The hepatitis B X-interacting protein (HBXIP) operates as a cofactor for phosphorylated survivin allowing it to bind and suppress activation of pro-caspase 9 (Marusawa et al., 2003, EMBO J. 22, 2729-2740). Other modes of action are discussed, too (Beltrami et al., 2004, J. Biol. Chem. 279, 2077-2084).
Survivin has attracted great intention as novel therapeutic target, because it is selectively expressed in cancer cells and it is required for their viability. Survivin is normally expressed during embryogenesis. Apart from the thyme, CD34+ bone-marrow-derived stem cells, placenta and the basal colonic epithelium, survivin is not detecTable in normal adult tissues, but is basically overexpressed in all transformed cells independent of their mitotic status. Expression is generally regulated in a cell-cycle dependent manner peaking at mitosis (Li et al. 1998, Nature 396, 580-584). Upregulation in G2/M phase compared to interphase can be more than 40-fold. Also, increased protein stability due to phosphorylation of Thr 34 by CDC2-cyclin-B1 may account for elevated survivin levels at mitosis. In the interphase, the protein level declines due to ubiquitin dependent proteolysis (Zhao et al., 2000, J Cell Sci. 113, 4363-71) to basal levels. It has been suggested that overexpression of survivin in cancer cells counteracts a default induction of apoptosis, overcomes the G2/M checkpoint and thus enforces progression of cells through mitosis (Li et al., 1998, Nature 396, 580-584).
In cell culture systems, inhibition of cell death by overexpression of survivin is well established (Ambrosini et al. 1997, Nat. Med. 3, 917-921; Tamm et al. 1998, Cancer Res. 58, 5315-5320; Mahotka et al., 1999, Cancer Res. 59, 6097-6102).
In vivo, survivin's role as inhibitor of apoptosis has been demonstrated in transgenic mice expressing survivin in the skin, which inhibited UVB induced apoptosis of the keratinocytes (Grossman at al., 2001, J. Clin. Invest. 108, 991-999). Apart from its role in cellular apoptosis, survivin plays a critical role in various aspects of mitosis. For example, knocking out survivin in homozygous survivin knock-out mice leads to 100% lethality (Uren et al. 2000, Curr. Biol. 10, 1319-1328; Conway et al., 2002, Gastroenterolgy 123, 619-631). Survivin has been found to be associated with various components of the mitotic apparatus, such as centrosomes, mictrotubules and the remnants of the spindle apparatus—the midbodies. Microtubule association is essential for survivin's anti-apoptotic action.
Survivin's dual role as apoptosis inhibitor and essential factor in cell division was demonstrated by targeted downregulation of survivin by transfecting HeLa cells with EPR-1 cDNA, which is complementary to survivin. Downregualtion of survivin by EPR-1 antisense resulted in increased apoptosis and inhibition of cell proliferation (Ambrosini et al., 1998, J. Biol. Chem. 273, 11177-11182). Other hallmarks of survivin ablation are mitotic arrest, polyploidy, defect centrosome replication, microtubule nucleation and mitotic spindle assembly/stability and inhibition of cell division. Most of these effects are exacerbated in a p53−/− mutant background (Beltrami et al., 2004, J. Biol. Chem. 279, 2077-2084; Carvalho et al, 2003, J. Cell. Sci. 116, 2987-2998; Lens et al., 2003, EMBO J. 22, 2934-2947). The pivotal role of survivin in mitosis is underscored by its association with the mitotic apparatus, including microtubules of the metaphase and anaphase spindle, and kinetochores of metaphase chromosomes (Beltrami et al., 2004, J. Biol. Chem. 279, 2077-2084). Survivin colocalizes with other chromosomal passenger proteins such as INCENP and Aurora B (Carvalho et al, 2003, J. Cell. Sci. 116, 2987-2998; Lens et al., 2003, EMBO J. 22, 2934-2947). Kinase activity of Aurora B is dependent upon interaction with surviving (Chen et al., 2003, J. Biol. Chem. 278, 486-490). It has been suggested that Aurora B kinase activity is essential to cytokinesis providing a mechanistic link between survivin and cell division (Chen et al., 2003, J. Biol. Chem. 278, 486-490). Two reports demonstrate that survivin is required for sustained the checkpoint arrest in response to lack of tension on kinetochores of sister chromatides. Survivin appears to be essential for the maintenance of checkpoint protein BubR1 at the kinetochores and mitotic arrest under protracted conditions of lack of tension at the kinetochores. Taxol, a microtubule stabilizing agent, allows attachment of microtubules to kinetochores, but prevents generation of tension. Normally taxol treated cells arrest in mitosis due to checkpoint activation mediated by kinetochore associated BubR1. Taxol treated Survivin depleted cells however manage to complete mitosis after a delay during which BubR1 is lost from the kinetochore. Nocodazol also prevents tension forming at the kinetochores but by preventing microtubule attachment. However depletion of Survivin has no effect on checkpoint activation and mitotic arrest induced by Nocodazol. Survivin is apparently not involved in monitoring kinetochore occupancy by microtubuli but instead required for checkpoint monitoring spindle tension excerted on the kinetochore. (Carvalho et al, 2003, J. Cell. Sci. 116, 2987-2998; Lens et al., 2003, EMBO J. 22, 2934-2947). Moreover it has been suggested that survivin serves as a crucial p53 dependent mitotic checkpoint protein required for genomic integrity and cytoprotection (Beltrami et al., 2004, J. Biol. Chem. 279, 2077-2084). Survivin may therefore be an important link between cell death and the regulation of cell division. Due to its dual role as inhibitor of apoptosis and promoter of mitosis survivin is an important factor in onset and progression of cancer as well as resistance to chemotherapeutic agents.
Its clinical role in cancer has been emphasized by detection of high levels of survivin in almost all tumour types. Elevated expression of survivin in tumours is associated with poor prognosis, increased cancer recurrence and resistance to therapy (Kawasaki et al., 1998, Cancer Res. 58, 5071-5074; Adida et al., 1998, Lancet 351, 882-883). Interestingly, lung and breast tumours express the highest levels of survivin. These tumours are generally associated with unfavourable prognosis due to early metastasizing and development of resistance to a number of mechanistically unrelated chemotherapeutic agents. Downregulation of survivin has been shown to sensitize tumor cells to DNA damaging agents such as etoposide (Li et al., 1999, Nature Cell Biology 1, 461-466; Olie et al., 2000, Cancer Res. 60, 2805-2809; Jiang et al., 2001, J. Cell. Biochem. 83, 342-354), cisplatin (Pennati et al., 2004, Oncogene 23, 386-394), doxorubicin (Zhou et al., 2002, J. Pharmacol. Exp. Ther. 303, 124-131) and radiotherapy (Pennati et al., 2003, J. Invest. Dermatol. 120, 648-654; Asanuma et al., 2002, Jpn. J. Cancer Res. 93, 1057-1062). Survivin depleted cells are particularly senetive to texol is also true for taxol (Zaffaroni et al., 2002, Cell. Mol. Life Sci. 59, 1406-1412; Ling et al., 2004, J. Biol. Chem. Epub ahead of print). Resistance to taxol and radiotherapy has been shown to correlate with the expression level of survivin (Zaffaroni et al., 2002, Cell. Mol. Life Sci. 59, 1406-1412; Rodel et al., 2003, Int. J. Radiat. Oncol. Biol. Phys. 55, 1341-1347) and sublethal concentrations of taxol has been shown to upregulate survivin expression significantly in MCF-7 breast cancer cells (Ling et al., 2004, J. Biol. Chem. Epub ahead of print). Survivin appears to be required for the function of the spindle checkpoint in response to taxol treatment (Carvalho et al, 2003, J. Cell. Sci. 116, 2987-2998; Lens et al., 2003, EMBO J. 22, 2934-2947). In the absence of survivin cells are therefore deprived of one of their natural resistance mechanisms that allows repair of the adverse effects of taxol on mitosis.
Interestingly, survivin also plays a critical role in angiogenesis. Survivin was found upregulated in angiogenically stimulated endothelium in vitro and in vivo (O'Connor et al., 2000, Am. J. Pathol. 156, 393-398; Tran et al., 1999, Biochem. Biophys. Res. Commun. 264, 781-788). Antisense targeting of survivin caused endothelial apoptosis and rapid involution of capillary-like vessels in vitro (Mesri et al., 2001a, Am. J. Pathol. 158, 1757-1765). Injection into human breast cancer xenografts of an adenovirus expressing a dominant negative version of survivin inhibited growth of established tumors. This was associated with apoptosis of both tumor cells and endothelial cells and a significant reduction in tumor derived blood vessels (Blanc-Brude et al., 2003, Clin. Cancer Res. 9, 2683-2692). Chemotherapy and radiotherapy targets both tumor cells and the proliferating endothelial cells of the tumor vasculature. Vascular endothelial growth factor (VEGF) has been shown to significantly reduce the proapoptotic potency of chemotherapy on vascular endothelial cells. This cytoprotection to drug toxicity has been linked to a VEGF mediated upregulation of survivin expression. Suppression of survivin activity abrogates the cytoprotective effect of VEGF to drugs that interfere with microtubule dynamics (Taxol) and damage DNA as well as protection against tumor necrosis factor α (Tran et al., 2002, Proc. Natl. Acad. Sci. USA 99, 4349-4354; Mesri et al., 2001a, Am. J. Pathol. 158, 1757-1765). In addition expression of a dominant negative survivin (T34A) protein in endothelial cells (HUVECC and DMVEC) resulted in massive induction of apoptosis (Blanc-Brude et al., 2003, Clin. Cancer Res. 9, 2683-2692).
Targeting survivin is increasingly being mentioned as having a dual anticancer activity by inducing tumor cell apoptosis and suppression of tumor associated angiogenesis (Altieri D C, 2003, Oncogene 22, 8581-8591).
Several therapeutic approaches using survivin as target have been initiated. The most promising ones comprise vaccination strategies, use of mutant survivin as dominant-negative antagonists, and application of survivin specific antisense oligonucleotides. Application of a replication deficient adenovirus expressing a dominant negative survivin mutant protein (Thr34-Ala) caused inhibited tumour growth in three distinct breast cancer xenograft models in mice. This adenovirus has shown in vivo efficacy in a breast cancer xenograft models and induced expression of survivin (T34A) in melanoma cells inhibited tumor growth in a melanoma xenograft model (Blanc-Brude et al., 2003, Clin. Cancer Res. 9, 2683-2692; Grossman et al., 2001 Proc. Natl. Sci. USA 98; 635-640). In cell cultures apoptosis was increased by binding of mutant survivin to CDC2-cyclin-B1 and thus preventing phosphorylation of wildtype survivin (Mesri et al., 2001b, J. Clin. Invest 108, 981-990). Some CDC2 antagonists like purvalanol A and flavopiridol, preventing survivin phospholylation, are currently being tested in clinical trials in combination with taxol (Schwartz et al., 2002, J. Clin. Oncol. 20, 2157-2170).
Several approaches using antisense oligonucleotides have shown that anti-survivin antisense oligonucleotides downregulate survivin in cell cultures, induce apoptosis and sensitize lung cancer cells and HeLa cells to the chemotherapeutic agent etoposide (Li et al., 1999, Nature Cell Biology 1, 461-466; Olie et al., 2000, Cancer Res. 60, 2805-2809; Jiang et al., 2001, J. Cell. Biochem. 83, 342-354). Inhibition of several cell lines with antisense oligo ISIS 28599, a mixed backbone 2′-O-MOE wingmer, resulted in multinucleated cells and induction of apoptosis (Chen at al., 2000, Neoplasia 2, 235-241). In a mouse liver regeneration model survivin mRNA was reduced 90% by the antisense oligonucleotide ISIS 114926 (Proceedings of the American Association for Cancer Research, vol. 42, 2001, abstract #2468). Intratumoral injection of antisense oligonucleotide ISIS 23722 reduced had limited effect on the growth rate of aggressive non-Hodgkin's lymphoma xengraft tumors in mice (Ansell et al., 2004, Leukemia—Epub ahead of print).
There are currently no therapeutic agents, which effectively inhibit the synthesis of survivin. Therefore, there is a longfelt need for agents inhibiting tumor cell growth by reducing survivin expression. In WO9822589 methods of modulating apoptosis with agents, that modulates the amount or activity of survivin and methods for reducing the severity of a pathological state mediated by survivin with such agents are disclosed. Such an agent is a construct encoding the EPR-1 coding strand, which is complementary to survivin but no specific antisense oligos are disclosed. WO0164741 discloses a “tet-off” promoter system regulating a survivin antisense mRNA transcript. However, this application does not disclose any antisense oligonucleotides.
Most of the oligonucleotides currently in clinical trials are based on the phosphorothioate chemistry from 1988, which was the first useful antisense chemistry to be developed. However, as it has become clear in recent years this chemistry has serious shortcomings that limit its clinical use. These include low affinity for their target mRNA, which negatively affects potency and puts restrictions on how small active oligonucleotides can be thus complicating manufacture and increasing treatment costs. Also, their low affinity translate into poor accessibility to the target mRNA thus complicating identification of active compounds. Finally, phosphorothioate oligonucleotides suffer from a range of side effects that narrow their therapeutic window.
To deal with these and other problems, much effort has been invested in creating novel analogues with improved properties. As depicted in the scheme 1 below, these include wholly artificial analogues such as PNA and Morpholino and more conventional DNA analogues such as boranosphosphates, N3′-P5′ phosphoroamidates and several 2′ modified analogues, such as 2′-F, 2′-O-Me, 2′-O-methoxyethyl (MOE) and 2′-O-(3-aminopropyl) (AP). More recently hexitol nucleic acid (HNA), 2′-F-arabino nucleic acid (2′-F-ANA) and D-cyclohexenyl nucleoside (CeNA) have been introduced.
Many of these analogues exhibit improved binding to complementary nucleic acids, improvements in bio-stability or they retain the ability to recruit a cellular enzyme, RNAseH, which is involved in the mode-of-action of many antisense compounds. None of them, however, combine all of these advantages and in many cases improvements in one of the properties compromise one or more of the other properties. Also, in many cases new complications have been noted which seriously limits the commercial value of some of the analogues. These include low solubility, complex oligomerisation chemistries, very low cellular up-take, incompatibility with other chemistries, etc.
Antisense oligonucleotides for modulation of survivin expression for treatment of diseases are disclosed in WO0018781 and WO0157059. These oligonucleotides are all between 18-20 bp in length and designed with the phosphorothioate or the MOE chemistry.
WO014655 discloses one single antisense oligonucleotide targeting Survivin and it is a fully modified phosphorthioate with some MOE nucleosides. The MOE chemistry has several limitations. It has only modest affinity, which only manifests when several MOE's are inserted en block into the oligo. MOE belongs to the family of 2′-modifications and it is well known, for this group of compound, that the antisense activity is directly correlated with RNA binding affinity in vitro. A MOE 20 bp gapmer (5MOE/PO-10PS-5MOE/PO) targeting c-raf has been reported to have an IC50 of about 20 nm in T24 cells and an MOE gapmer targeting PKC-a has been reported to have an IC50 of 25 nm in A549 cells. In comparison, phosphorthioate compounds used in antisense experiments typically exhibit IC50 in the 150 nm range. (Stein, Kreig, Applied Antisense Oligonucleotide Technology, Wiley-Liss, 1988, p 87-90)
WO03027244, filed subsequent to the present invention, discloses a 20-mer phosphorthioate antisense oligonucleotides targeting survivin which show down regulation at very high concentrations (for example compound 903 showed 51% protein reduction at 200 nM).
It is a principal object of the present invention to provide novel oligomeric compounds, against the survivin mRNA. The compounds of the invention have been found to exhibit an decreased IC50 (thus increased activity), thereby facilitating an effective treatment of a variety of cancer diseases in which the expression of survivin is implied as a causative or related agent. As explained in the following, this objective is best achieved through the utilisation of a super high affinity chemistry termed LNA (Locked Nucleic Acid).
The present invention is directed to oligomeric compounds, particularly LNA antisense oligonucleotides, which are targeted to a nucleic acid encoding survivin and which modulate the expression of the survivin. This modulation was particularly a very potent down regulation survivin mRNA as well as elicitation of apoptotic response. The LNA-containing oligomeric compounds can be as low as an 8-mer and certainly highly active as a 16-mers, which is considerably shorter than the reported antisense compounds targeting survivin. These 16-mer oligomeric compounds have an IC50 in the sub-nanomolar range. The invention enables a considerable shortening of the usual length of an antisense oligomers (from 20-25 mers to, e.g., 8-16 mers) without compromising the affinity required for pharmacological activity. As the intrinsic specificity of an oligo is inversely correlated to its length, such a shortening will significantly increase the specificity of the antisense compound towards its RNA target. Furthermore, it is anticipated that shorter oligomeric compounds have a higher biostability and cell permeability than longer oligomeric compounds. For at least these reasons, the present invention is a considerable contribution to the art.